Im stuck with my q4. I think problem is the bleeding procedure. I changed some hydro lines and with that the powersteering oil as well. And now there is yellow 4x4 warning light and no four wheel driving.
How exactly I have to make this "fooling solenoid thing" or how i can manually bleed the system? I tried to loose the return line back of the car where is the viscomatic unit, but nothing really happened.

You cannot bleed the system by putting a straight 12VDC on the regulating solenoid.

The easiest way is the solution made bij the "Fool" resistor. In this case the viscomaticsystem thinks the systempressure hasn't been reached yet while it actually has. In this case the overpressurevalve will open thus bleeding the system...

Hello, has anyone found a replacement pressure sensor for viscomatic? Just found out that the thread of the sensor is not metric. Its 3/8 UNF (or was it UNC?) with 24 threads per inch. Does anyone know the specs of the sensor, for example pressure scale?

Vehje wrote:Hello, has anyone found a replacement pressure sensor for viscomatic? Just found out that the thread of the sensor is not metric. Its 3/8 UNF (or was it UNC?) with 24 threads per inch. Does anyone know the specs of the sensor, for example pressure scale?

I am not sure exactly which sensor you are referring to - do you have the part number?

Sorry for my bad English: There is only one pressure sensor in the viscomatic group. Part number is 5894237 and I figured it out that there is no one who would recognize this sensor or know something about it. So I started to solve the problem:

Thread of the sensor is 3/8 UNF (24TIP(threads per inch)). Sensor has three connectors (incoming voltage 5V, ground and signal to the viscomatic control unit ) In my Q4 the viscomatic charge valve awakes when the signal voltage coming from the pressure sensor drops to 3,7 V. When the signal voltage of the pressure sensor goes to 4,5 V, will charge valve close.

So I connected mechanical pressure sensor to the hydraulic group and the pressure was sailing between 50-65bar(should be between 82-95bar). I bought a sensor that sends 4,5v when the pressure is 130bar(max) and connected a potentiometer resistance between the +5V and the signal wire. By screwing the potentiometer(that gives some voltage from 5V to the signal wire) I was able to get the pressure between ~78-97bar.

The thread of the sensor is so weird (never in italian cars before) I had to go to the local american-car shop to get a proper fit to the thread.

Very good work with the pressure sensor Vehje, excited to see that you're solving this problem!

It's only a matter of time when others will need to do it too. Pressure sensor for the Viscomatic, piston position sensor, and the hydraulic valves, will all not last forever, so reproduction is needed at some point.

No it didn´t solve the problem. It´s too difficult to try to solve the problem without tester error codes. Last summer I went to the workshop to read the fault codes and it cost me 75 euros. Too expensive... The fault codes were from the pressure sensor and steering angle sensor.

Vehje wrote:No it didn´t solve the problem. It´s too difficult to try to solve the problem without tester error codes. Last summer I went to the workshop to read the fault codes and it cost me 75 euros. Too expensive... The fault codes were from the pressure sensor and steering angle sensor.

So you may have solved the pressure sensor issue, while the steering angle sensor may still have a fault?

I have described what I did to my steering angle sensor in another thread, I will try to find it. You should be able to measure what the voltage is at different steering wheel positions. Did the workshop give you documentation of the error codes?